Backup CB play bodes well for soon-to-be-tested secondary

Cornerback Chris Culliver has followed an impressive rookie season with a strong training camp. (AP)

In a 10-minute span during today’s practice, a trio of backup cornerbacks – Chris Culliver, Perrish Cox and Tramaine Brock – took turns making first-string-quality plays.

First, Culliver stepped in front of wideout Brett Swain along the right sideline and picked off a pass from Josh Johnson. Moments later, Cox made an acrobatic pick – tapping both feet in bounds along the sideline to intercept an Alex Smith pass intended for Ted Ginn, Finally, Brock jumped in front of tight end Konrad Rueland and took Colin Kaepernick’s pass in the other direction.

The flurry of picks from the potential No. 3, No. 4 and No. 5 cornerbacks was a promising sign for a secondary that figures to need all hands on deck this season.

If last season’s playoffs were a harbinger of things to come, get ready for some serious passing. In the divisional playoffs, Drew Brees attempted 63 passes against San Francisco. In the NFC Championship Game, Eli Manning threw 58 passes.

That’s a lot. In fact, the 121 passes in back-to-back games are the most attempted against a defense in NFL history, according to the Elias Sports Bureau.

As safety Donte Whitner noted today, teams increasingly began abandoning the run against the Niners and took to the air. The 49ers ranked first in the NFL in rushing defense (77.3 yards) and allowed three rushing touchdowns, the fewest since the NFL went to a 16-game schedule in 1978.

Last year, NFL teams attempted 17,410 passes and 13,971 runs (a pass-run percentage of 55-45). Against the 49ers, teams attempted 579 passes and 353 runs (pass-run percentage of 62-38). This season, the 49ers will face the top three teams in passes attempted last year in the Lions, Saints and Patriots, who each averaged more than 38 passes a game.

“We expect a lot of passes, especially after last year,” Whitner said. “Coming into last year … we didn’t know what to expect from offenses. Now we know what to expect. We expect them to us to test us early in the run and then if we do what we’re supposed to do, they’re going to abandon it and go to a lot of screens, short passes, long downfield passes. We have to prepare for everything, but we have to understand we’re not going get 40 runs a game.”

And the 49ers could be better equipped to handle the aerial onslaught this season with the continued development of Culliver, last year’s third-round pick, and the signing of Cox, a fifth-round pick of the Broncos in 2010 who didn’t play last year due to legal issues. In March, Cox was found not guilty of sexual-assault charges.

Both Culliver and Cox have had excellent training camps.

On Saturday, Cox ran stride for stride with Ted Ginn along the sideline and batted away a well-placed, 40-yard throw from Alex Smith. Today, he was involved in the pick parade with Culliver and Brock.

“He’s a quick guy, he’s always around the football,” safety Dashon Goldson said of Cox. “We were talking about it today. I think he has a lot of potential. He’ll help this football team. He’s still got a lot to learn, but he’s showing up on film. He’s around the ball all the time, getting his hands on balls. That’s a big thing in the secondary.”